Systems and methods for simulating ground effect

ABSTRACT

Ground effect acting on an aerial vehicle, such as an unmanned aerial vehicle, may be simulated by discharging a gas around propeller blades of the aerial vehicle while the propeller blades are rotating. For example, a gas, such as air, may be discharged at or near the tip of the propeller blades with enough velocity to disrupt the airflow around the blade tips, thereby altering the sound generated by rotation of the propeller blade.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/975,491, filed Dec. 18, 2015, the contents of which are incorporatedherein by reference in its entirety.

BACKGROUND

Vehicle traffic around residential areas continues to increase.Historically, vehicle traffic around homes and neighborhoods wasprimarily limited to automobile traffic. However, the recent developmentof aerial vehicles, such as unmanned aerial vehicles, has resulted in arise of other forms of vehicle traffic. For example, hobbyists may flyunmanned aerial vehicles in and around neighborhoods, often within a fewfeet of a home. Likewise, there is discussion of electronic-commerceretailers, and other entities, delivering items directly to a user'shome using unmanned aerial vehicles. As a result, such vehicles may beinvited to navigate into a backyard, near a front porch, balcony, patio,and/or other locations around the residence to complete delivery ofpackages.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number appears.

FIG. 1 depicts a view of an aerial vehicle, according to animplementation.

FIG. 2 depicts a motor mounted to a motor arm, according to animplementation.

FIG. 3 depicts a detailed view of a motor and the magnets of the rotorof the motor, according to an implementation.

FIG. 4 depicts a view of another aerial vehicle, according to animplementation.

FIG. 5 depicts a view of an arm of an aerial vehicle with gas canisters,according to an implementation.

FIG. 6 depicts a view of another aerial vehicle, according to animplementation.

FIG. 7 is a flow diagram illustrating an example ground effectsimulation process, according to an implementation.

FIG. 8 is a block diagram illustrating various components of an unmannedaerial vehicle control system, according to an implementation.

DETAILED DESCRIPTION

This disclosure describes methods and apparatus for simulating groundeffects for propellers of aerial vehicles to reduce the sound generatedby those propellers during operation. Ground effect is a well-knownphenomenon that occurs when an aerial vehicle flies at a level that isapproximately at or below the length of the aerial vehicles wingspan orpropeller diameter. When flying at those low levels, the ground disruptsthe airflow around the propellers or wings. This alteration results inlower induced drag, which increases the speed and lift of the aerialvehicle, and/or lift generated by the rotation of propellers. Theincreased lift from the rotating propellers results in the aerialvehicle being able to maintain the low altitude while rotating thepropellers at a slower speed. In addition, the disruption of airflowcaused by ground effect may also influence the formation of vortices.The slower rotation of the propellers and/or the disrupted formation ofthe vortices reduces the sound generated by the aerial vehicle when theaerial vehicle is close enough to the ground to experience groundeffect.

The implementations described herein simulate ground effect onpropellers of an aerial vehicle when the aerial vehicle is at altitudesabove those that are typical for ground effect so that sound generatedby the aerial vehicle can be reduced or otherwise altered. For example,a gas, such as air, may be discharged at or near the tip of thepropeller blades with enough velocity to disrupt the airflow around theblade tips. The disrupted airflow may impact the lift generated by therotation of the propeller, disrupt formation of vortices at the bladetip, and/or to cause formed vortices to be displaced an amountsufficient to reduce blade vortex interaction (“BVI”). BVI occurs when afollowing propeller blade passes through or interacts with vorticesformed by a leading propeller blade. When a following propeller bladepasses through formed vortices, the propeller blade disrupts thevortices and the disruption generates sound.

By disrupting the airflow around the tip of the propeller blade, thesound generated from the rotation of the propeller blade is reduced. Forexample, in the instance of increased lift, the rotational speed of thepropeller blade may be reduced, thereby reducing sound generated by therotation of the propeller blade. In other examples, the disruptedformation of vortices and/or the displacement of formed vortices mayreduce BVI sounds.

In some implementations, the gas is discharged when the aerial vehicleis at low altitudes (but higher than altitudes in which actual groundeffect occurs), such as during item delivery, to reduce the soundsgenerated by the aerial vehicle. For example, when the aerial vehicle isbetween approximately twenty-five feet and approximately six feet, gasmay be discharged at or near the tip of the propeller blades to simulateground effect and reduce the sound generated by the aerial vehicleduring item delivery.

FIG. 1 is a view of an aerial vehicle 101 configured for sound controlby simulating ground effects while the aerial vehicle is operating. Thepropellers 102-1, 102-2, 102-3, and 102-4 are powered by motors andspaced about a body 104 of the aerial vehicle 101 as part of apropulsion system. A control system (not shown), which may be positionedwithin the body 104, is utilized for controlling the motors for flyingthe aerial vehicle 101, as well as controlling other operations of theaerial vehicle 101. Each of the motors may be rotated at differentspeeds, thereby generating different lifting forces by the differentpropellers 102.

The motors may be of any type and of a size sufficient to rotate thepropellers 102 at speeds sufficient to generate enough lift to aeriallypropel the aerial vehicle 101 and any items engaged by the aerialvehicle 101 so that the aerial vehicle 101 can navigate through the air,for example, to deliver an item to a location. While the example of FIG.1 includes four motors and propellers, in other implementations, more orfewer motors and/or propellers may be utilized for the propulsion systemof the aerial vehicle 101. Likewise, in some implementations, the motorsand/or propellers may be positioned at different locations and/ororientations on the aerial vehicle 101. Alternative methods ofpropulsion may also be utilized in addition to the propellers andpropeller motors. For example, engines, fans, jets, turbojets, turbofans, jet engines, and the like may be used in combination with thepropellers and propeller motors to propel the aerial vehicle.

The body 104 or frame of the aerial vehicle 101 may be of any suitablematerial, such as graphite, carbon fiber, and/or aluminum. In thisexample, the body 104 of the aerial vehicle 101 includes four motor arms108-1, 108-2, 108-3, and 108-4 that are coupled to and extend from thebody 104 of the aerial vehicle 101. The propellers 102 and correspondingpropeller motors are positioned at the ends of each motor arm 108. Insome implementations, all of the motor arms 108 may be of approximatelythe same length while, in other implementations, some or all of themotor arms may be of different lengths. Likewise, the spacing betweenthe two sets of motor arms may be approximately the same or different.

In some implementations, one or more sensors 106 configured to measuresound at the aerial vehicle is included on the aerial vehicle 101. Thesensors 106 may be at any location on the aerial vehicle 101. Forexample, a sensor 106 may be positioned on each motor arm 108 andadjacent to the propeller 102 and/or propeller motor so that differentsensors can measure different sounds generated at or near the differentpropellers 102. In another example, one or more sensors may bepositioned on the body 104 of the aerial vehicle 101. The sensors 106may be any type of sensors capable of measuring sound and/or soundwaves. For example, the sensor may be a microphone, transducer,piezoelectric sensor, an electromagnetic pickup, an accelerometer, anelectro-optical sensor, an inertial sensor, etc.

As discussed in further detail below, one or more of the propellers 102may include a gas discharge cavity 150. The cavity 150 may extend thelength of the propeller 102 and be configured to allow a gas to passthrough the cavity and exit one or more openings at the end of thecavity near a tip of the propeller 102. For example, the propeller 102-4includes a gas discharge cavity 150 that extends down the middle of thesurface area of the propeller 102-4 and includes a plurality of openings156 at the end of the cavity. In other implementations, there may be asingle opening at the end of cavity 150. The opening of the cavity isaligned so that the discharged gas is blown outward from the tip of thepropeller, as illustrated in the expanded view.

The cavity 150 and openings 156 may be formed on the interior of thepropellers 102, on an upper surface area of the propellers, on a lowersurface area of the propellers, along the leading edge of thepropellers, along the trailing edge of the propellers, and/or at anyother location along the propellers.

A gas, such as air, hydrogen, helium, nitrogen, oxygen, argon, krypton,xenon, sulfur hexafluoride, etc. may be discharged so that is exits theopenings 156 at the end of the propeller. The gas is discharged withenough velocity to disrupt the airflow around the propeller blade,thereby reducing the sound generated by rotation of the propeller blade.For example, if the area of the circle in which the propeller 102rotates is 1 meter squared (“m²”) and the lifting force to be generatedby rotation of the propellers is approximately 50 Newton (“N”), or 50kilogram meters per second squared (“kg*m/sec²), the flow velocity ofthe discharged gas to simulate a ground effect, can be roughly estimatedfrom an equal amount of pressure, or 50 Pascal (Pa). So:

${\frac{1}{2}\rho*v^{2}} = {{50\mspace{20mu}{Pa}} = {50\frac{kg}{m*\sec^{2}}}}$${\rho*v^{2}} = {{100\mspace{14mu}{Pa}} = {100\frac{kg}{m*\sec^{2}}}}$$v = {{\rho*\sqrt{100\mspace{14mu}{Pa}}} = {\rho*\sqrt{100\frac{kg}{m*\sec^{2}}}}}$Where ρ=1.25 kg/m³, the density of air, ν is computed as 12.5 m/s, whereν is the flow velocity of the gas exiting the openings of the cavity.

While a flow velocity of gas 190 out of the openings 156 of 12.5 m/swill simulate ground effect, in some implementations, the flow velocityof the gas may be less and still alter the sound generated by rotationof the propeller. Likewise, in some implementations, using gasses ofdifferent densities may, in addition to simulating ground effect, alterthe generated sound as a result of varying densities of the gasses.

In some implementations, the aerial vehicle 101 may begin discharginggas at a first velocity (e.g., 50% of the velocity needed to fullysimulate ground effect) and utilize the sensors to measure the soundaround the aerial vehicle 101, and/or a reduction in generated sound bycomparing a sound measured by the sensors 106 prior to discharge of thegas and sound measured during discharge of the gas 190. If the sound isbelow a defined threshold (allowable sound level), the velocity at whichthe gas is being discharged may be maintained or reduced. However, ifthe measured sound is not below the allowable sound level, the velocityof the discharged gas may be increased to further reduce the soundgenerated by the rotation of the propellers. In some implementations,the sensors 106 positioned at or near each propeller may independentlymeasure sound and the velocity of the gas being discharged from thatpropeller may be adjusted based on the measured sound at the propeller.As such, the gas discharge and sound alteration may be independentlycontrolled at each propeller of an aerial vehicle.

As noted above, when a propeller rotates, vortices are generated at thetip of the propeller blade and those vortices generate sound, especiallywhen a following blade passes through the formed vortices (i.e., BVI).By discharging a gas at the tip of the propeller blade, therebydisrupting the airflow around the propeller blade, the formation of thetip vortices may be disrupted (e.g., the formed vortices may be smallerand/or less in number), such that the resulting sound is reduced.Likewise, the velocity of the discharged gas may push the formedvortices away from the path of the propeller blades so that a followingpropeller blade does not pass through the formed vortices. Thedisplacement of formed vortices reduces BVI, thereby further reducingthe sound generated by the rotation of the propeller.

While the implementations of the aerial vehicle discussed herein utilizepropellers to achieve and maintain flight, in other implementations, theaerial vehicle may be configured in other manners. For example, theaerial vehicle may be a combination of both propellers and fixed wings.In such configurations, the aerial vehicle may utilize one or morepropellers to enable takeoff, and/or landing, and a fixed wingconfiguration or a combination wing and propeller configuration tosustain flight while the aerial vehicle is airborne. In someimplementations, one or more of the propulsion mechanisms (e.g.,propellers and motors) may have a variable axes such that it can rotatebetween vertical and horizontal orientations.

FIG. 2 depicts a diagram of a motor 200 coupled to a motor arm 208,according to an implementation. In this example, the motor may be anytype of motor 200, such as a brushless DC motor, in which a rotor 204rotates about a stator (not shown in FIG. 2) to drive rotation of apropeller 202. The motor 200 includes a base 206 that is affixed to amotor arm 208 that secures the motor 200 to the motor arm 208 of theaerial vehicle. The base 206 of the motor 200 may be affixed to themotor arm 208 by a series or type of screws, clamps, mounts, fasteners,etc.

The propeller 202 is affixed to the rotor 204 of the motor 200 such thatthe propeller 202 rotates with a rotation of the rotor 204. For example,in some configurations, a propeller shaft 205 may extend from the top ofthe rotor down the center of the stator and the rotor 204 and thepropeller 202 may be affixed to the shaft. In other configurations, thepropeller 202 may be directly coupled or clamped to the rotor 204.

Positioned within the motor arm 208 is one or more gas canisters 255that contain gas that may be discharged. The gas canister 255 is affixedto a cavity 252 (e.g., a tube) that extends from the gas canister 255 upthe shaft 205 and couples at a joint 254 to the cavity 250 formed in orcoupled to the propeller 202. The joint 254 may be any type ofconnection that enables rotation of the propeller 202 and allows gasdischarged from the gas canister 255 to pass through the cavity 252 andthrough the cavity 250 so that the gas 290 exits the openings 256 at theend of the cavity 250.

The discharge of gas 290 from the gas canister 255 may be controlled bya gas discharge controller, discussed below. The gas dischargecontroller may, for example, determine if one or more operatingconditions satisfy a criterion and open or close the gas canister 255and/or the openings 256 to enable or disable the discharge of gas 290from the gas canister 255 and out the openings 256 that are positionedproximate the tip of the propeller blades of the propeller 202.

Operating conditions that may be monitored by the gas dischargecontroller include, but are not limited to, an altitude of the aerialvehicle, a sound level around the aerial vehicle, a frequency spectrumof the sound around the aerial vehicle, a position of the aerialvehicle, or a distance between the aerial vehicle and an object (e.g.,human, building, automobile, etc.). Similarly, the criterion are relatedto the monitored operating conditions. For example, one criterion may bean altitude of the aerial vehicle, such that if the aerial vehicle isbelow a defined altitude (e.g., twenty-five feet) the criterion issatisfied and gas may be discharged to reduce a sound generated by theaerial vehicle.

In another example, an allowable sound level and/or frequency spectrummay be defined and if the sound measured around the aerial vehicleexceeds either the sound level and/or the frequency spectrum, thecriterion may be satisfied and the gas discharged. In still anotherexample, the position of the aerial vehicle may be monitored and if theaerial vehicle is positioned in an area populated by humans, it may bedetermined that the criterion is satisfied and the gas discharged. In asimilar manner, if the aerial vehicle is within a defined distance of anobject (e.g., human, building, automobile, etc.) it may be determinedthat the criterion is satisfied and the gas discharged to reduce thesound generated by the aerial vehicle.

As will be appreciated any one or more conditions may be satisfied andany number of criteria may be considered in determining whether todischarge gas to reduce the sound of the aerial vehicle. Likewise, insome implementations, multiple criteria may be specified for one or moreconditions and as those criteria are satisfied, a velocity of thedischarged gas may be adjusted. For example, a first criterion may besatisfied when the condition of altitude of the aerial vehicle passesbelow fifty feet such that gas is discharged at a first velocity. Whenthe altitude of the aerial vehicle falls below twenty-five feet a secondcriterion may be satisfied and the gas discharged at a second, highervelocity.

In some implementations, the gas canister may be replaceable. Forexample, an access point 251 may be incorporated into the motor arm 208that enables access and replacement of the gas canister. In someimplementations, the replacement of the gas canister may be performedusing automation, such as a robotic unit configured to remove a used gascanister and insert a filled gas canister while the aerial vehicle isnot airborne (e.g., being loaded with a payload and/or while charging),or during operation of the aerial vehicle.

In some implementations, the gas canister may be a single use gascanister in which the gas is discharged when it is determined that theaerial vehicle has dropped below a defined altitude and is delivering apayload into an area that is populated by humans. In such animplementation, the gas may be stored in the gas canister under pressurethat will result in the gas being discharged at a velocity that will, atleast partially, simulate ground effect and alter the sound generated bythe propellers of the aerial vehicle. Likewise, because it may only bebeneficial to alter the sound generated by the aerial vehicle when theaerial vehicle is below a defined altitude, and a time required todeliver a payload and ascend above the defined altitude can beestimated, the pressure and the amount of gas to be contained in thecanister can be pre-determined. Specifically, it can be determined howmuch gas at a particular pressure is needed so that gas can bedischarged out of the openings 256 of the cavity at a specified velocityduring the time that the aerial vehicle is below the defined altitude.

In other implementations, rather than, or in addition to a gas canister,the aerial vehicle may include one or more scoops that allow air to flowinto the scoops as the aerial vehicle is aerially navigating. Thecollected air may then be stored in canisters on the aerial vehicle orallowed to pass through the cavity and discharged out the openings. Insuch implementations, a pump may be utilized to control the flow orvelocity of the air that is discharged through the openings of thecavity.

FIG. 3 depicts a detailed view of a motor 300 and the magnets 312 of therotor 304 of the motor, according to an implementation. A brushless DCmotor typically includes a base 308, a stator 309, and a rotor 304. Thebase 308 is generally used to affix the motor 300 to an aerial vehicle,such as a UAV. Likewise, the stator 309 is coupled to the base. Thestator 309, also known as an armature, includes an electromagneticassembly 310, and is typically configured in a cylindrical manner, asshown in FIG. 3, and remains stationary on the base.

The rotor 304 is also configured in a cylindrical manner such that itextends above the base 308 and substantially encompasses and rotatesaround the stator 309. On an interior surface of the rotor are a seriesof magnets 312 that are used to drive rotation of the rotor.Specifically, as is known in the art, when a current is applied to theelectromagnets 310, it causes alternating polarities of theelectromagnets which attract or repel the magnets 312 affixed to theinterior surface of the rotor 304. The attraction/repulsion of themagnets 312 by the electromagnets 310 of the stator 309 cause the rotor304 to rotate. A propeller 302 is also affixed to the rotor 304 androtates with the rotor 304.

As illustrated, the cavity 352-1 may, in one implementation, extend upthrough the base 308 of the motor 300 and through a central portion ofthe stator 309. Likewise, a shaft 305 that is coupled to and extendsdown from the top of the rotor 304 and toward the base may include acavity 352-2 that couples with the cavity 352-1 so that gas can passthrough the base 308, the stator 309 and the rotor 304 up to thepropeller 302. The propeller 302 includes a cavity 350 that is formed inand/or coupled to the propeller 302 that is configured to receive gasfrom the cavity 352 and allow the gas to pass toward an end of thepropeller 302 and exit the openings 356 at the tip of the propellerblades of the propeller 302.

While the example illustrated in FIG. 3 shows the cavity passing throughthe center of the motor 300, in other implementations the cavity may notpass through the motor. For example, the gas canister may be positionedon a top of the motor such that the gas is discharged from the gascanister and directly into the cavity of the propeller. In such animplementation, the gas canister may rotate with a rotation of the motorand the rotation of the propeller.

FIG. 4 illustrates a view of another aerial vehicle 400, according to animplementation. As illustrated, the aerial vehicle 400 includes aperimeter frame 404 that includes a front wing 420, a lower rear wing424, an upper rear wing 422, and two horizontal side rails 430-1, 430-2.The horizontal side rails 430 are coupled to opposing ends of the frontwing 420 and opposing ends of the upper rear wing 422 and lower rearwing 424. In some implementations, the coupling may be with a cornerjunction. In other implementations, the wings and the side rails may beformed of a single mold, or coupled directly together.

The components of the perimeter frame 404, such as the front wing 420,lower rear wing 424, upper rear wing 422, and/or side rails 430-1, 430-2may be formed of any one or more suitable materials, such as graphite,carbon fiber, aluminum, titanium, etc., or any combination thereof. Inthe illustrated example, the components of the perimeter frame 404 ofthe aerial vehicle 400 are each formed of carbon fiber and joined at thecorners using corner junctions.

The front wing 420, lower rear wing 424, and upper rear wing 422 arepositioned in a tri-wing configuration and each wing provides lift tothe aerial vehicle 400 when the aerial vehicle is moving in a directionthat includes a horizontal component. For example, the wings may eachhave an airfoil shape that causes lift due to the airflow passing overthe wings during horizontal flight.

In some implementations, to increase the stability and control of theaerial vehicle 400, one or more winglets 421, or stabilizer arms, mayalso be coupled to and included as part of the perimeter frame 404. Inthe example illustrated with respect to FIG. 4, there are two frontwinglets 421-1 and 421-2 mounted to the underneath side of the frontleft corner junction and the front right corner junction 431-2,respectively. The winglets 421 extend in a downward directionapproximately perpendicular to the front wing 420 and side rails 430.Likewise, the two rear corner junctions are also formed and operate aswinglets providing additional stability and control to the aerialvehicle 400 when the aerial vehicle 400 is moving in a direction thatincludes a horizontal component.

Coupled to the interior of the perimeter frame 404 is a central frame407. The central frame 407 includes a hub 408 and motor arms 405 thatextend from the hub 408 and couple to the interior of the perimeterframe 404. In this example, there is a single hub 408 and four motorarms 405-1, 405-2, 405-3, and 405-4. Each of the motor arms 405 extendfrom approximately a corner of the hub 408 and couple or terminate intoa respective interior corner of the perimeter frame. Like the perimeterframe 404, the central frame 407 may be formed of any suitable material,such as graphite, carbon fiber, aluminum, titanium, etc., or anycombination thereof. In this example, the central frame 407 is formed ofcarbon fiber and joined at the corners of the perimeter frame 404 at thecorner junctions.

Lifting motors 406 are coupled at approximately a center of each motorarm 405 so that the lifting motor 406 and corresponding liftingpropeller 402 are within the substantially rectangular shape of theperimeter frame 404. In one implementation, the lifting motors 406 aremounted to an underneath or bottom side of each motor arm 405 in adownward direction so that the propeller shaft of the lifting motor thatmounts to the lifting propeller 402 is facing downward. In otherimplementations, as illustrated in FIG. 4, the lifting motors 406 may bemounted to a top of the motor arms 405 in an upward direction so thatthe propeller shaft of the lifting motor that mounts to the liftingpropeller 402 is facing upward. In this example, there are four liftingmotors 406-1, 406-2, 406-3, 406-4, each mounted to an upper side of arespective motor arm 405-1, 405-2, 405-3, and 405-4.

In some implementations, multiple lifting motors may be coupled to eachmotor arm 405. For example, while FIG. 4 illustrates a quad-copterconfiguration with each lifting motor mounted to a top of each motorarm, a similar configuration may be utilized for an octo-copter. Forexample, in addition to mounting a motor 406 to an upper side of eachmotor arm 405, another lifting motor may also be mounted to anunderneath side of each motor arm 405 and oriented in a downwarddirection. In another implementation, the central frame may have adifferent configuration, such as additional motor arms. For example,eight motor arms may extend in different directions and a lifting motormay be mounted to each motor arm.

The lifting motors may be any form of motor capable of generating enoughrotational speed with the lifting propellers 402 to lift the aerialvehicle 400 and any engaged payload, thereby enabling aerial transportof the payload.

Mounted to each lifting motor 406 is a lifting propeller 402. Thelifting propellers 402 may be any form of propeller (e.g., graphite,carbon fiber) and of a size sufficient to lift the aerial vehicle 400and any payload engaged by the aerial vehicle 400 so that the aerialvehicle 400 can navigate through the air, for example, to deliver apayload to a delivery location. For example, the lifting propellers 402may each be carbon fiber propellers having a dimension or diameter oftwenty-four inches. While the illustration of FIG. 4 shows the liftingpropellers 402 all of a same size, in some implementations, one or moreof the lifting propellers 402 may be different sizes and/or dimensions.Likewise, while this example includes four lifting propellers 402-1,402-2, 402-3, 402-4, in other implementations, more or fewer propellersmay be utilized as lifting propellers 402. Likewise, in someimplementations, the lifting propellers 402 may be positioned atdifferent locations on the aerial vehicle 400. In addition, alternativemethods of propulsion may be utilized as “motors” in implementationsdescribed herein. For example, fans, jets, turbojets, turbo fans, jetengines, internal combustion engines, and the like may be used (eitherwith propellers or other devices) to provide lift for the aerialvehicle.

In addition to the lifting motors 406 and lifting propellers 402, theaerial vehicle 400 may also include one or more thrusting motors 410 andcorresponding thrusting propellers 412. The thrusting motors andthrusting propellers may be the same or different than the liftingmotors 406 and lifting propellers 402. For example, in someimplementations, the thrusting propellers may be formed of carbon fiberand be approximately eighteen inches long. In other implementations, thethrusting motors may utilize other forms of propulsion to propel theaerial vehicle. For example, fans, jets, turbojets, turbo fans, jetengines, internal combustion engines, and the like may be used (eitherwith propellers or with other devices) as the thrusting motors.

The thrusting motors and thrusting propellers may be oriented atapproximately ninety degrees with respect to the perimeter frame 404 andcentral frame 407 of the aerial vehicle 400 and utilized to increase theefficiency of flight that includes a horizontal component. For example,when the aerial vehicle 400 is traveling in a direction that includes ahorizontal component, the thrusting motors may be engaged to provide ahorizontal thrust force via the thrusting propellers to propel theaerial vehicle 400 horizontally. As a result, the speed and powerutilized by the lifting motors 406 may be reduced. Alternatively, inselected implementations, the thrusting motors may be oriented at anangle greater or less than ninety degrees with respect to the perimeterframe 404 and the central frame 407 to provide a combination of thrustand lift.

In the example illustrated in FIG. 4, the aerial vehicle 400 includestwo thrusting motors 410-1, 410-2 and corresponding thrusting propellers412-1, 412-2. Specifically, in the illustrated example, there is a frontthrusting motor 410-1 coupled to and positioned near an approximatemid-point of the front wing 420. The front thrusting motor 410-1 isoriented such that the corresponding thrusting propeller 412-1 ispositioned inside the perimeter frame 404. The second thrusting motor iscoupled to and positioned near an approximate mid-point of the lowerrear wing 424. The rear thrusting motor 410-2 is oriented such that thecorresponding thrusting propeller 412-2 is positioned inside theperimeter frame 404.

While the example illustrated in FIG. 4 illustrates the aerial vehiclewith two thrusting motors 410 and corresponding thrusting propellers412, in other implementations, there may be fewer or additionalthrusting motors and corresponding thrusting propellers. For example, insome implementations, the aerial vehicle 400 may only include a singlerear thrusting motor 410 and corresponding thrusting propeller 412. Inanother implementation, there may be two thrusting motors andcorresponding thrusting propellers mounted to the lower rear wing 424.In such a configuration, the front thrusting motor 410-1 may be includedor omitted from the aerial vehicle 400. Likewise, while the exampleillustrated in FIG. 4 shows the thrusting motors oriented to positionthe thrusting propellers inside the perimeter frame 404, in otherimplementations, one or more of the thrusting motors 410 may be orientedsuch that the corresponding thrusting propeller 412 is oriented outsideof the protective frame 404.

The perimeter frame 404 provides safety for objects foreign to theaerial vehicle 400 by inhibiting access to the lifting propellers 402from the side of the aerial vehicle 400, provides protection to theaerial vehicle 400, and increases the structural integrity of the aerialvehicle 400. For example, if the aerial vehicle 400 is travelinghorizontally and collides with a foreign object (e.g., wall, building),the impact between the aerial vehicle 400 and the foreign object will bewith the perimeter frame 404, rather than a propeller. Likewise, becausethe frame is interconnected with the central frame 407, the forces fromthe impact are dissipated across both the perimeter frame 404 and thecentral frame 407.

As illustrated in the expanded view, the motor arms 405 may include oneor more openings 456-1, 452-2 from the cavities 452 that run through themotor arms that are configured to allow a gas to pass through the cavityand exit the openings. In this example, rather than, or in addition todischarging gas from cavities positioned on or in the propeller blades,the cavities are positioned in or on the motor arms and the openings ofthe cavities are positioned so that the discharged gas is directedtoward the blade tips of the propeller 402. In the illustrated example,the motor 406 and the propeller 402 are positioned above the motor arm405 and the openings 456-1, 456-2 are oriented so that the dischargedgas 490 is directed upward toward an underneath side of the tip of thepropeller blade 402. In other implementations, the openings may extendfurther along the motor arms 405 so that discharged gas is directed toall and/or other portions of the propeller blade of the propeller 402.

In this example, the openings 456-1, 456-2 are positioned at either endof the motor arm 405 where the tip of the propeller passes over themotor arm 405. When the gas is discharged, the discharge may becontrolled so that the gas is only discharged while the propeller bladeis passing over the motor arm 405. In other implementations, the motorarm may include a perimeter ring that extends from the motor arm 405 ina circular shape that is approximately the same diameter, or slightlysmaller than the diameter of the propeller 402. In such a configuration,the openings may extend around the perimeter ring and the gas may bedischarged from one or more openings along the propeller ring that arealigned with the position of the propeller blade as it rotates. Inanother example, the gas may be discharged from all openingssimultaneously. Alternatively, the gas may be discharged prior to thepropeller blade passing over the openings and/or the gas may bedischarged subsequent to the propeller blade passing over the openings.

If the motor 406 is mounted to the underneath side of the motor arm 405such that the propeller is beneath the motor arm 405, the openings 456of the cavity 452 may be positioned on the underneath side of the motorarm and aligned so that the gas is discharged downward toward thepropeller blade.

The perimeter frame 404 also provides a surface upon which one or morecomponents of the aerial vehicle 400 may be mounted. Alternatively, orin addition thereto, one or more components of the aerial vehicle may bemounted or positioned within portions of the perimeter frame 404. Forexample, as illustrated in FIG. 5, one or more gas canisters may bepositioned within one or more of the side rails 430 and cavities may beformed in the frame between the gas canisters and the openings in themotor arm so that gas discharged from the gas canisters will travel toand exit the openings in the motor arms 405.

Other components, such as antennas may be mounted on or in the frame ofthe aerial vehicle 400. For example, wireless antennas, cameras, time offlight sensors, accelerometers, inclinometers, distance-determiningelements, gimbals, Global Positioning System (GPS) receiver/transmitter,altimeters, radars, illumination elements, speakers, and/or any othercomponent of the aerial vehicle 400 or the aerial vehicle control system(discussed below), etc., may be mounted to or in the perimeter frame404. Likewise, identification or reflective identifiers may be mountedto the perimeter frame 404 to aid in the identification of the aerialvehicle 400.

In some implementations, the perimeter frame 404 may also include apermeable material (e.g., mesh, screen) that extends over the top and/orlower surface of the perimeter frame 404 enclosing the central frame,lifting motors, and/or lifting propellers.

An aerial vehicle control system 414 is also mounted to the centralframe 407. In this example, the aerial vehicle control system 414 ismounted to the hub 408 and is enclosed in a protective barrier. Theprotective barrier may provide the control system 414 weather protectionso that the aerial vehicle 400 may operate in rain and/or snow withoutdisrupting the control system 414. In some implementations, theprotective barrier may have an aerodynamic shape to reduce drag when theaerial vehicle is moving in a direction that includes a horizontalcomponent. The protective barrier may be formed of any materialsincluding, but not limited to, graphite-epoxy, Kevlar, and/orfiberglass. In some implementations, multiple materials may be utilized.For example, Kevlar may be utilized in areas where signals need to betransmitted and/or received.

Likewise, the aerial vehicle 400 includes one or more power modules (notshown). The power modules may be positioned anywhere on the aerialvehicle 400, such as inside the side rails 430-1, 430-2. In otherimplementations, the power modules may be mounted or positioned at otherlocations of the aerial vehicle. The power modules for the aerialvehicle may be in the form of battery power, solar power, gas power,super capacitor, fuel cell, alternative power generation source, or acombination thereof. The power module(s) are coupled to and providepower for the aerial vehicle control system 414, the lifting motors 406,the thrusting motors 410, and the payload engagement mechanism (notshown).

In some implementations, one or more of the power modules may beconfigured such that it can be autonomously removed and/or replaced withanother power module while the aerial vehicle is landed or in flight.For example, when the aerial vehicle lands at a location, the aerialvehicle may engage with a charging member at the location that willrecharge the power module.

As mentioned above, the aerial vehicle 400 may also include a payloadengagement mechanism (not shown). The payload engagement mechanism maybe configured to engage and disengage items and/or containers that holditems (payload). In this example, the payload engagement mechanism ispositioned beneath and coupled to the hub 408 of the frame 404 of theaerial vehicle 400. The payload engagement mechanism may be of any sizesufficient to securely engage and disengage a payload. In otherimplementations, the payload engagement mechanism may operate as thecontainer in which it contains item(s). The payload engagement mechanismcommunicates with (via wired or wireless communication) and iscontrolled by the aerial vehicle control system 414.

FIG. 5 illustrates an example of a side rail 530 of the aerial vehicleillustrated in FIG. 4. In this example, four gas canisters 532 may beinstalled in the interior 536 of the side rail 530. For example, the gascanisters 532 may be affixed to a gas canister holder 534 that fitswithin the interior 536 of the side rail 530. In some implementations,the interior 536 may include grooves or ridges that are configured toreceive the gas canister holder 534 and/or to provide communicationbetween the gas canisters 532 and a gas discharge controller (discussedbelow) that controls the discharge of gas from the gas canisters 532. Inthe example illustrated in FIG. 5, the gas canister holder 534 andcorresponding gas canisters 532 fit within the interior 536 of the siderail 530. When positioned in the interior of the side rail, the openingsof the gas canisters 532 align with a cavity 550 that is formed in theside rail 530 so that the gas from the canisters can be discharged outof the canisters and through the cavity 550.

In other implementations, the side rail 530 may include an opening onthe top, bottom, or side of the side rail 530 that is configured toreceive the gas canister holder 534 and gas canisters 532. For example,the side rail 530 may include an opening in the underneath side of theside rail 530 that is approximately the same size and shape as the gascanister holder 534. The gas canisters 532 may be passed through theopening into the interior 536 of the side rail and the gas canisterholder 534 may fit into the opening and be secured to the side rail,thereby enclosing the gas canisters into the side rail 530 and securingthe openings of the gas canisters 532 into the cavity 550. In such animplementation, the gas canisters 532 may be removed and replacedwithout having to remove the side rail 530 from the aerial vehicle.

In still another example, the side rail 530 may function as a side railand a gas canister. Rather than having a separate gas canister holderand gas canisters that may be inserted or removed from the side rail,the gas canisters 532 may be permanently incorporated into the side railand the side rail(s) may be removed from the aerial vehicle when the gashas been discharged and replaced with another side rail that containsgas. In still another example, the side rail 530 may include an inputport through which gas can be filled back into the canisters so that thecanisters and/or the side rail 530 can be reused.

FIG. 6 is a view of another aerial vehicle 601, according to animplementation. In this example, the aerial vehicle 601 includes fourpropellers 618, each of which is rotated by a motor 616. The aerialvehicle also includes a frame 604, which may be a single unit. The frame604 may be formed of any type of material, such as carbon fiber, Kevlar,titanium, wood, etc.

Components may be mounted to the frame 604. For example, the motors 616are mounted to the frame, the aerial vehicle control system 610, whichmay include the gas discharge controller(s), is mounted to the frame604, and one or more gas canisters 655 are mounted to the frame 604. Theframe is designed to encompass the components of the aerial vehicle 601,including the propellers 618 and provide a protective barrier around theaerial vehicle 601. Other components discussed herein, such as powermodules, sensors, etc., may likewise be included on the aerial vehicle601 illustrated in FIG. 6.

In this example the frame 604 also includes or has attached thereto, acavity that allows gas to pass from the gas canisters 655 to one or moreopenings that are proximate the propeller 618 blade tips. For example,the openings may extend around an interior of the frame 604 where theinterior of the frame 604 is near the propellers 618. Alternatively, orin addition thereto, the openings may extend along an underneath side ofthe motor arms 605 and be oriented so that gas exiting the openings isdirected toward the propeller 618 that is rotating below the motor arm605.

In implementations in which the openings extend along the interior ofthe frame 604 at areas proximate the propeller blades, the openings maybe positioned and oriented so that the gas exiting the openings isdirected downward toward the upper side of the tips of the propellerblade, upwards toward the underneath side of the tips of the propellerblade, or inward and horizontal with the propeller blades.

For example, referring first to the expanded view 630-1, the openings656 are aligned along the interior of the frame 604 and positionedbeneath the height of the propeller blade such that when the propellerblade is rotating it passes above the openings 656. Likewise, theopenings 656 are oriented upward toward the propeller 618 so that thegas 690-1 exiting the openings is directed upward toward an underneathside of the propeller 618. In another example, the openings may bepositioned above the height of the propeller blade such that when thepropeller blade is rotating it passes below the openings. In such anexample, the openings are oriented downward toward the propeller 618 sothat the gas 690-1 exiting the openings is directed toward an upper sideof the propeller 618.

In another example, as illustrated in the expanded view 630-2, multiplesets of openings 656, 658 may be positioned along the interior of theframe 604 of the aerial vehicle 601 and positioned so that gas exitingthe openings is directed toward the propeller 618 as it rotates. Forexample, the openings 656 are aligned along the interior of the frame604 and positioned beneath the height of the propeller blade such thatwhen the propeller blade 618 is rotating it passes above the openings656. Likewise, the openings 656 are oriented upward toward the propeller618 so that the gas 690-1 exiting the openings is directed upward towardan underneath side of the propeller 618. In addition, the second set ofopenings 658 are positioned above the height of the propeller blade suchthat when the propeller blade is rotating it passes below the openings.In such an example, the openings are oriented downward toward thepropeller 618 so that the gas 690-1 exiting the openings is directedtoward an upper side of the propeller 618. By including two sets ofopenings, the tip of the propeller blade passes between the two sets ofopenings and gas can be discharged from both sets of openingssimultaneously, from just the upper set of openings, or from just thelower set of openings.

In still another example, referring to expanded view 630-3, the openings670 may be positioned along the interior of the frame 604 of the aerialvehicle 601 so that they are approximately in-line or at the same heightas the propeller 618. In such an example, the openings 670 may beoriented toward the propeller 618 so that gas 690-3 discharged from theopening passes over both the upper side and the lower side of thepropeller blade 618.

While the examples discussed with respect to FIG. 6 illustratepositioning of a set of openings above the propeller blade, below thepropeller blade, both above and below the propeller blade, or at anapproximate same height as the propeller blade, it will be appreciatedthat any combination of positions may be utilized with theimplementations described herein. For example, three sets of openingsmay be included on the interior of the frame—one set above thepropeller, one set below the propeller, and one set at approximately thesame height as the propeller. Likewise, the openings may have anyvariety of orientations. For example, the openings from the set ofopenings positioned above the propeller blade may be oriented downwardtoward the propeller blade and at an angle such that the gas exiting thepropeller blade is traveling downward and in a direction that is counterto the rotation of the propeller blade. In other implementations, theopenings may be oriented differently. In some implementations, thedirection or orientation of openings within a set of openings may vary,thereby generating gas flow around the propeller that is turbulent.

In each of the implementations discussed herein, the gas dischargecontroller may control the discharge of gas by, for example, opening orclosing the gas canister to either allow or prohibit gas to pass throughthe cavity and out the openings of the cavity. In other examples, thegas discharge controller may control the discharge of gas by controllingthe openings at the ends of the cavity. For example, the openings at theend of the cavity, such as the openings 656 illustrated in FIG. 6 may beselectively opened or closed by the gas discharge controller to eitherallow or prohibit the discharge of gas through the opening. For example,rather than allowing gas to exit all of the openings 656 positionedaround the interior of the frame 604 of the aerial vehicle, the gasdischarge controller may receive propeller position information from theaerial vehicle control system indicating a position of each propellerblade as it rotates. Based on the position information, the gasdischarge controller may open and close the openings of the cavity sothat gas is only discharged from openings that are proximate thepropeller blade tip. In such an example, the openings are opened andclosed as the propeller rotates so that gas is discharged toward thepropeller blade as it rotates.

FIG. 7 is a flow diagram illustrating an example ground effectsimulation process 700, according to an implementation. This process,and each process described herein, may be implemented by thearchitectures described herein or by other architectures. The process isillustrated as a collection of blocks in a logical flow graph. Some ofthe blocks represent operations that can be implemented in hardware,software, or a combination thereof. In the context of software, theblocks represent computer-executable instructions stored on one or morecomputer readable media that, when executed by one or more processors,perform the recited operations. Generally, computer-executableinstructions include routines, programs, objects, components, datastructures, and the like that perform particular functions or implementparticular abstract data types.

The computer readable media may include non-transitory computer readablestorage media, which may include hard drives, floppy diskettes, opticaldisks, CD-ROMs, DVDs, read-only memories (ROMs), random access memories(RAMs), EPROMs, EEPROMs, flash memory, magnetic or optical cards,solid-state memory devices, or other types of storage media suitable forstoring electronic instructions. In addition, in some implementations,the computer readable media may include a transitory computer readablesignal (in compressed or uncompressed form). Examples of computerreadable signals, whether modulated using a carrier or not, include, butare not limited to, signals that a computer system hosting or running acomputer program can be configured to access, including signalsdownloaded through the Internet or other networks. Finally, the order inwhich the operations are described is not intended to be construed as alimitation, and any number of the described operations can be combinedin any order and/or in parallel to implement the process.

The example process 700 begins by determining one or more operatingconditions of the aerial vehicle, as in 702. The operating conditionsmay be any measurable aspect of the aerial vehicle and/or theenvironment around the aerial vehicle. For example, operating conditionsmay include, but are not limited to, an altitude of the aerial vehicle,a sound level around the aerial vehicle, a frequency spectrum of soundaround the aerial vehicle, a position of the aerial vehicle, a distancebetween the aerial vehicle and an object (e.g., human, building), etc.

A determination is then made as to whether the operating condition(s)satisfies one or more criteria, as in 704. The criterion may be anydefined criterion corresponding to an operating condition. For example,a criterion may be a defined altitude and the criterion satisfied whenthe aerial vehicle is flying below the defined altitude. In someimplementations, the example process 700 may determine whether multiplecriteria are satisfied, such as the aerial vehicle being below a definedaltitude during a particular time of day or within a particular area,before the example process proceeds to block 708.

The criterion may vary for different aerial vehicles, differentlocations, different times of day, different days of the week, etc. Forexample, the defined altitude may be different for rural areas thanurban areas. As another example, the defined altitude may be lower insuburban areas during weekday work hours (e.g., 09:00-17:00) than duringnon-work hours.

If it is determined that one or more of the operating conditions satisfyone or more criteria, the sound around the aerial vehicle is measured,as in 708. Based on the measured sound, a determination is made as towhether the sound is above an allowable sound level and/or outside adefined frequency spectrum, as in 708. The allowable sound level may beany defined sound level and may vary for different aerial vehicles,different locations, different times of day, etc. Likewise, the definedfrequency spectrum may be any defined frequency spectrum and may alsovary.

If it is determined that the sound around the aerial vehicle is notabove the allowable sound level and not outside the defined frequencyspectrum, the example process 700 returns to block 702 and continues.However, if it is determined that the sound around the aerial vehicle isabove the allowable sound level and/or outside the defined frequencyspectrum, gas is discharged from one or more openings on the aerialvehicle that are proximate to one or more propeller blades of the aerialvehicle, as in 710. As discussed above, the gas is discharged with avelocity sufficient to disrupt the airflow around the propeller blade.For example, the velocity of the discharged gas may disrupt theformation of vortices at the blade tip and/or to displace formedvortices out of the path of a following propeller to reduce BVI. Bydisrupting the airflow around the propeller blade, the sound generatedby the rotation of the propeller is reduced and/or otherwise altered.For example, the relative and/or absolute amplitudes of variousfrequency components of the sound may be altered. In someimplementations, the gas may be discharged from openings positioned onor proximate to each of the propeller blades of the aerial vehicle. Inother implementations, the gas may only be discharged from or proximateto one or more propeller blades of the aerial vehicle.

As the gas is discharged, the example process returns to block 702. Whengas discharge is initiated, the discharge may continue until theoperating conditions no longer satisfy the criterion. Likewise, thevelocity of the discharged gas may continue to be increased until themeasured sound around the aerial vehicle is below the allowable soundlevel and/or within the defined frequency spectrum. When the sound isbelow the allowable sound level and/or within defined frequencyspectrum, the gas may continue to be discharged at an approximatelycontinuous velocity until the criteria are no longer satisfied.

The example process may be performed any time the aerial vehicle isoperational. For example, if an aerial vehicle is aerially navigating toa delivery destination where it will deliver a package that contains acustomer ordered item, the example process 700 may be performed. As theaerial vehicle approaches the delivery destination, the altitude (anoperating condition) may be monitored. When the aerial vehicle descendsto an altitude that is below a defined altitude (e.g., 25 feet), theexample process may cause the sound around the aerial vehicle to bemonitored and determine if the measured sound is above an allowablesound level and/or outside a defined frequency range. If it isdetermined that the measured sound is above an allowable sound leveland/or outside a defined frequency range, gas may be discharged towardone or more propeller blades of the aerial vehicle to reduce orotherwise alter the sound generated by the rotation of the propellerblades. Reducing or otherwise altering the sound generated by therotating propeller blades, reduces or otherwise alters the total soundaround the aerial vehicle, thereby making delivery of the item by theaerial vehicle quieter.

FIG. 8 illustrates a block diagram of components of one systems 800 forcontrolling sound generated by an aerial vehicle, in accordance with animplementation. The system 800 of FIG. 8 includes an aerial vehiclecontrol system 810 of an aerial vehicle, such as those discussed above,and may also include a data processing system 870 connected via anetwork 880. The aerial vehicle control system 810 includes a processor812, a memory 814 and a transceiver 816, as well as a plurality ofsensors 820, and a gas discharge controller 806. In someimplementations, the aerial vehicle control system may include multiplegas discharge controllers, each one controlling discharge of gasproximate a respective propeller. In other implementations, a single gasdischarge controller may control discharge of gas from all openings onthe aerial vehicle.

The processor 812 may be configured to perform any type or form ofcomputing function, including but not limited to the execution of theexample process 700 and/or the other implementations and methodsdiscussed herein. For example, the processor 812 may control any aspectsof the operation of the aerial vehicle control system 810 and the one ormore computer-based components thereon, including but not limited to thetransceiver 816, the sensors 820, and/or the gas discharge controller806. The aerial vehicle control system 810 may likewise generateinstructions for conducting various operations, e.g., for operating oneor more rotors, motors, rudders, ailerons, flaps or other componentsprovided on the aerial vehicle. The aerial vehicle control system 810further includes one or more memory or storage components 814 forstoring any type of information or data, e.g., instructions foroperating the aerial vehicle, propeller position information, criterion,or information or data captured by one or more of the sensors 820 (e.g.,operating conditions).

The transceiver 816 may be configured to enable the aerial vehiclecontrol system 810 to communicate through one or more wired or wirelessmeans, e.g., wired technologies such as Universal Serial Bus (or “USB”)or fiber optic cable, or standard wireless protocols, such as Bluetooth®or any Wireless Fidelity (or “Wi-Fi”) protocol, such as over the network880 or directly.

The sensors 820 may include any components or features for determiningone or more operating conditions relating to the aerial vehicle,including extrinsic information or data or intrinsic information ordata. As is shown in FIG. 8, the sensors 820 may include, but are notlimited to, a Global Positioning System (“GPS”) receiver or sensor 821,a compass 822, a speedometer 823, an altimeter 824, a thermometer 825, abarometer 826, a hygrometer 827, a gyroscope 828, and/or a microphone832. The GPS sensor 821 may be any device, component, system orinstrument adapted to receive signals (e.g., trilateration data orinformation) relating to a position of the aerial vehicle from one ormore GPS satellites of a GPS network (not shown). The compass 822 may beany device, component, system, or instrument adapted to determine one ormore directions with respect to a frame of reference that is fixed withrespect to the surface of the Earth (e.g., a pole thereof). Thespeedometer 823 may be any device, component, system, or instrument fordetermining a speed or velocity of the aerial vehicle, and may includerelated components (not shown) such as pitot tubes, accelerometers, orother features for determining speeds, velocities, or accelerations.

The altimeter 824 may be any device, component, system, or instrumentfor determining an altitude of the aerial vehicle, and may include anynumber of barometers, transmitters, receivers, range finders (e.g.,laser or radar) or other features for determining heights. Thethermometer 825, the barometer 826 and the hygrometer 827 may be anydevices, components, systems, or instruments for determining local airtemperatures, atmospheric pressures, or humidities within a vicinity ofthe aerial vehicle. The gyroscope 828 may be any mechanical orelectrical device, component, system, or instrument for determining anorientation, e.g., the orientation of the aerial vehicle. For example,the gyroscope 828 may be a traditional mechanical gyroscope having atleast a pair of gimbals and a flywheel or rotor. Alternatively, thegyroscope 828 may be an electrical component such as a dynamically tunedgyroscope, a fiber optic gyroscope, a hemispherical resonator gyroscope,a London moment gyroscope, a microelectromechanical sensor gyroscope, aring laser gyroscope, or a vibrating structure gyroscope, or any othertype or form of electrical component for determining an orientation ofthe aerial vehicle. The microphone 832 may be any type or form oftransducer (e.g., a dynamic microphone, a condenser microphone, a ribbonmicrophone, a crystal microphone) configured to convert acoustic energyof any intensity and across any or all frequencies into one or moreelectrical signals, and may include any number of diaphragms, magnets,coils, plates, or other like features for detecting and recording suchenergy. The microphone 832 may also be provided as a discrete component,or in combination with one or more other components, e.g., an imagingdevice, such as a digital camera. Furthermore, the microphone 832 may beconfigured to detect and record acoustic energy from any and alldirections.

Those of ordinary skill in the pertinent arts will recognize that thesensors 820 may include any type or form of device or component fordetermining a condition within a vicinity of the aerial vehicle inaccordance with the present disclosure. For example, the sensors 820 mayinclude one or more air monitoring sensors (e.g., oxygen, ozone,hydrogen, carbon monoxide or carbon dioxide sensors), infrared sensors,ozone monitors, pH sensors, magnetic anomaly detectors, metal detectors,radiation sensors (e.g., Geiger counters, neutron detectors, alphadetectors), altitude indicators, depth gauges, accelerometers or thelike, as well as one or more imaging devices (e.g., digital cameras),and are not limited to the sensors 821, 822, 823, 824, 825, 826, 827,828, 832 shown in FIG. 8.

The data processing system 870 includes one or more physical computerservers 872 having a plurality of data stores 874 associated therewith,as well as one or more computer processors 876 provided for any specificor general purpose. For example, the data processing system 870 of FIG.8 may be independently provided for the exclusive purpose of receiving,analyzing or storing sounds, gas discharge locations/altitudes,resulting sound measurements, and/or other information or data receivedfrom the aerial vehicle control system 810. The servers 872 may beconnected to or otherwise communicate with the data stores 874 and theprocessors 876. The data stores 874 may store any type of information ordata, including but not limited to sound information or data, and/orinformation or data regarding operating conditions, etc. The servers 872and/or the computer processors 876 may also connect to or otherwisecommunicate with the network 880, as indicated by line 878, through thesending and receiving of digital data. For example, the data processingsystem 870 may include any facilities, stations or locations having theability or capacity to receive and store information or data, such asmedia files, in one or more data stores, e.g., media files received fromthe aerial vehicle control system 810, or from one another, or from oneor more other external computer systems (not shown) via the network 880.In some implementations, the data processing system 870 may be providedin a physical location. In other such implementations, the dataprocessing system 870 may be provided in one or more alternate orvirtual locations, e.g., in a “cloud”-based environment. In still otherimplementations, the data processing system 870 may be provided onboardone or more aerial vehicles, including but not limited to the aerialvehicle that contains the aerial vehicle control system 810.

The network 880 may be any wired network, wireless network, orcombination thereof, and may comprise the Internet in whole or in part.In addition, the network 880 may be a personal area network, local areanetwork, wide area network, cable network, satellite network, cellulartelephone network, or combination thereof. The network 880 may also be apublicly accessible network of linked networks, possibly operated byvarious distinct parties, such as the Internet. In some implementations,the network 880 may be a private or semi-private network, such as acorporate or university intranet. The network 880 may include one ormore wireless networks, such as a Global System for MobileCommunications (GSM) network, a Code Division Multiple Access (CDMA)network, a Long Term Evolution (LTE) network, or some other type ofwireless network. Protocols and components for communicating via theInternet or any of the other aforementioned types of communicationnetworks are well known to those skilled in the art of computercommunications and, thus, need not be described in more detail herein.

The computers, servers, devices and the like described herein have thenecessary electronics, software, memory, storage, databases, firmware,logic/state machines, microprocessors, communication links, displays orother visual or audio user interfaces, printing devices, and any otherinput/output interfaces to provide any of the functions or servicesdescribed herein and/or achieve the results described herein. Also,those of ordinary skill in the pertinent art will recognize that usersof such computers, servers, devices and the like may operate a keyboard,keypad, mouse, stylus, touch screen, or other device (not shown) ormethod to interact with the computers, servers, devices and the like, orto “select” an item, link, node, hub or any other aspect of the presentdisclosure.

The aerial vehicle control system 810 or the data processing system 870may use any web-enabled or Internet applications or features, or anyother client-server applications or features including E-mail or othermessaging techniques, to connect to the network 880, or to communicatewith one another, such as through short or multimedia messaging service(SMS or MMS) text messages. For example, the aerial vehicle controlsystem 810 may be adapted to transmit information or data in the form ofsynchronous or asynchronous messages to the data processing system 870or to any other computer device in real time or in near-real time, or inone or more offline processes, via the network 880. The protocols andcomponents for providing communication between such devices are wellknown to those skilled in the art of computer communications and neednot be described in more detail herein.

The data and/or computer executable instructions, programs, firmware,software and the like (also referred to herein as “computer executable”components) described herein may be stored on a computer-readable mediumthat is within or accessible by computers or computer components such asthe processor 812 or the processor 876, or any other computers orcontrol systems utilized by the aerial vehicle control system 810 or thedata processing system 870, and having sequences of instructions which,when executed by a processor (e.g., a central processing unit, or“CPU”), cause the processor to perform all or a portion of thefunctions, services and/or methods described herein. Such computerexecutable instructions, programs, software, and the like may be loadedinto the memory of one or more computers using a drive mechanismassociated with the computer readable medium, such as a floppy drive,CD-ROM drive, DVD-ROM drive, network interface, or the like, or viaexternal connections.

Some implementations of the systems and methods of the presentdisclosure may also be provided as a computer-executable program productincluding a non-transitory machine-readable storage medium having storedthereon instructions (in compressed or uncompressed form) that may beused to program a computer (or other electronic device) to performprocesses or methods described herein. The machine-readable storagemedia of the present disclosure may include, but is not limited to, harddrives, floppy diskettes, optical disks, CD-ROMs, DVDs, ROMs, RAMs,erasable programmable ROMs (“EPROM”), electrically erasable programmableROMs (“EEPROM”), flash memory, magnetic or optical cards, solid-statememory devices, or other types of media/machine-readable medium that maybe suitable for storing electronic instructions. Further,implementations may also be provided as a computer executable programproduct that includes a transitory machine-readable signal (incompressed or uncompressed form). Examples of machine-readable signals,whether modulated using a carrier or not, may include, but are notlimited to, signals that a computer system or machine hosting or runninga computer program can be configured to access, or include signals thatmay be downloaded through the Internet or other networks.

Although the disclosure has been described herein using exemplarytechniques, components, and/or processes for implementing the systemsand methods of the present disclosure, it should be understood by thoseskilled in the art that other techniques, components, and/or processesor other combinations and sequences of the techniques, components,and/or processes described herein may be used or performed that achievethe same function(s) and/or result(s) described herein and which areincluded within the scope of the present disclosure.

For example, although some of the implementations disclosed hereinreference the use of unmanned aerial vehicles to deliver payloads tocustomers, those of ordinary skill in the pertinent arts will recognizethat the systems and methods disclosed herein are not so limited, andmay be utilized in connection with any type or form of aerial vehicle(e.g., manned or unmanned) having fixed or rotating wings for anyintended industrial, commercial, recreational or other use.

It should be understood that, unless otherwise explicitly or implicitlyindicated herein, any of the features, characteristics, alternatives ormodifications described regarding a particular implementation herein mayalso be applied, used, or incorporated with any other implementationdescribed herein, and that the drawings and detailed description of thepresent disclosure are intended to cover all modifications, equivalentsand alternatives to the various implementations as defined by theappended claims. Also, the drawings herein are not drawn to scale.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey in apermissive manner that certain implementations could include, or havethe potential to include, but do not mandate or require, certainfeatures, elements and/or steps. In a similar manner, terms such as“include,” “including” and “includes” are generally intended to mean“including, but not limited to.” Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more implementations or that one or moreimplementations necessarily include logic for deciding, with or withoutuser input or prompting, whether these features, elements and/or stepsare included or are to be performed in any particular implementation.

Disjunctive language, such as the phrase “at least one of X, Y, or Z,”or “at least one of X, Y and Z,” unless specifically stated otherwise,is otherwise understood with the context as used in general to presentthat an item, term, etc., may be either X, Y, or Z, or any combinationthereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is notgenerally intended to, and should not, imply that certainimplementations require at least one of X, at least one of Y, or atleast one of Z to each be present.

Unless otherwise explicitly stated, articles such as “a” or “an” shouldgenerally be interpreted to include one or more described items.Accordingly, phrases such as “a device configured to” are intended toinclude one or more recited devices. Such one or more recited devicescan also be collectively configured to carry out the stated recitations.For example, “a processor configured to carry out recitations A, B andC” can include a first processor configured to carry out recitation Aworking in conjunction with a second processor configured to carry outrecitations B and C.

Language of degree used herein, such as the terms “about,”“approximately,” “generally,” “nearly” or “substantially,” as usedherein, represent a value, amount, or characteristic close to the statedvalue, amount, or characteristic that still performs a desired functionor achieves a desired result. For example, the terms “about,”“approximately,” “generally,” “nearly” or “substantially” may refer toan amount that is within less than 10% of, within less than 5% of,within less than 1% of, within less than 0.1% of, and within less than0.01% of the stated amount.

Although the disclosure has been described and illustrated with respectto illustrative implementations thereof, the foregoing and various otheradditions and omissions may be made therein and thereto withoutdeparting from the spirit and scope of the present disclosure.

The invention claimed is:
 1. A computer-implemented method, comprising:under control of one or more computing systems configured withexecutable instructions, determining an operating condition of an aerialvehicle; determining that the operating condition satisfies a criterion;and in response to determining that the operating condition satisfiesthe criterion, causing a discharge of a gas through a cavity of theaerial vehicle and into at least a path of a propeller blade of theaerial vehicle to be initiated.
 2. The computer-implemented method ofclaim 1, wherein the gas is discharged from an opening in the cavityformed along the propeller blade.
 3. The computer-implemented method ofclaim 1, wherein: the gas is discharged from an opening of the cavity;the cavity is part of a frame of the aerial vehicle; and the opening ofthe cavity is proximate a tip of the propeller blade.
 4. Thecomputer-implemented method of claim 3, wherein the opening of thecavity of the aerial vehicle is at least one of: below the propellerblade and oriented such that the gas is discharged upward toward thepropeller blade; above the propeller blade and oriented such that thegas is discharged downward toward the propeller blade; or aligned withthe propeller blade and oriented such that the gas is discharged towardthe propeller blade.
 5. The computer-implemented method of claim 3,wherein the operating condition is representative of at least one of analtitude of the aerial vehicle, a sound level around the aerial vehicle,a frequency spectrum of sound around the aerial vehicle, a position ofthe aerial vehicle, or a distance between the aerial vehicle and anobject.
 6. The computer-implemented method of claim 1, wherein the gasis discharged with a velocity sufficient to alter a sound generated by arotation of the propeller blade.
 7. The computer-implemented method ofclaim 1, further comprising: subsequent to the discharge of the gasbeing initiated, further monitoring the operating condition of theaerial vehicle; determining that the operating condition does notsatisfy the criterion; and in response to determining that the operatingcondition is not satisfied, causing the discharge of the gas to beterminated.
 8. The computer-implemented method of claim 1, furthercomprising: in response to determining that the operating conditionsatisfies the criterion, causing the gas to discharge around at least aportion of a plurality of propeller blades of the aerial vehicle.
 9. Anaerial vehicle control system, comprising: a gas discharge controllerconfigured to at least: monitor an operating condition of an aerialvehicle; determine that the operating condition satisfies a criterion;and subsequent to the determination that the operating conditionsatisfies the criterion, cause a discharge of a gas through a cavity ofthe aerial vehicle and into a path of a propeller of the aerial vehicleto be initiated.
 10. The aerial vehicle control system of claim 9,further comprising: a sensor communicatively coupled to the gasdischarge controller; wherein the gas discharge controller monitors theoperating condition based at least in part on information received fromthe sensor; and wherein the operating condition is representative of atleast one of an altitude of the aerial vehicle, a sound level around theaerial vehicle, a frequency of sound around the aerial vehicle, ageographic location of the aerial vehicle, or a distance between theaerial vehicle and an object.
 11. The aerial vehicle control system ofclaim 9, wherein the criterion is representative of at least one of: analtitude, a sound level, a frequency of a sound, a geographic location,or a distance.
 12. The aerial vehicle control system of claim 9, whereinthe gas discharge controller is further configured to at least:subsequent to the discharge of the gas being initiated, further monitorthe operating condition of the aerial vehicle; determine that theoperating condition satisfies a second criterion; and subsequent to thedetermination that the operating condition satisfies the secondcriterion and the discharge of the gas being initiated, cause a rate ofdischarge of the gas to be increased.
 13. The aerial vehicle controlsystem of claim 9, wherein the gas is from a pump or a canister.
 14. Theaerial vehicle control system of claim 9, wherein the gas exits thecavity at an opening.
 15. The aerial vehicle control system of claim 9,wherein the gas discharge controller is further configured to at least:receive rotation information that is representative of at least afrequency of a rotation of the propeller; and cause the discharge of thegas to be synchronized with the frequency of the rotation of thepropeller.
 16. The aerial vehicle control system of claim 9, wherein thegas discharge controller is further configured to at least: furthermonitor the operating condition of the aerial vehicle; determine thatthe operating condition is not satisfied; and cause the discharge of thegas to be restricted subsequent to the determination that the operatingcondition is not satisfied.
 17. The aerial vehicle control system ofclaim 16, wherein the discharge of the gas is restricted at least inpart by the gas discharge controller causing at least one opening of thecavity to be obstructed.
 18. The aerial vehicle control system of claim9, further comprising: a microphone communicatively coupled to the gasdischarge controller; and wherein the operating condition is monitoredbased at least in part on sound information from the microphone, and thecriterion is representative of at least one of a sound frequency or asound level.
 19. The aerial vehicle control system of claim 18, furthercomprising: an altimeter communicatively coupled to the gas dischargecontroller; and wherein the gas discharge controller is furtherconfigured to at least: determine a second operating condition based atleast in part on altitude information from the altimeter; and prior tocausing the discharge of the gas to be initiated, determine that thesecond operating condition satisfies a second criterion, wherein thesecond criterion is representative of an altitude.
 20. A gas dischargecontroller comprising: one or more processors; and a memory storingprogram instructions that when executed by the one or more processorscause the one or more processors to perform acts comprising: monitor anoperating condition of an aerial vehicle; determine that the operatingcondition satisfies a criterion; and subsequent to the determinationthat the operating condition satisfies the criterion, cause a dischargeof a gas through a cavity of the aerial vehicle and into a path of apropeller of the aerial vehicle to be initiated.
 21. The gas dischargecontroller of claim 20, wherein the program instructions when executedby the one or more processors further cause the one or more processorsto further perform acts comprising: subsequent to the discharge of thegas being initiated, further monitor the operating condition of theaerial vehicle; determine that the operating condition does not satisfythe criterion; and subsequent to the determination that the operatingcondition does not satisfy the criterion, cause the discharge of the gasto be restricted.